Learn Spanish (Latin America): Las latas tienen carne congelada.

It comes from the regular verb congelar (to freeze). To make the past participle for an -ar verb, you drop the -ar and add -ado. This gives us the base form congelado.

Why does it end in -a (congelada) if the regular past participle ending is -ado?

When you use a past participle as an adjective to describe a noun, it has to match that noun's gender (masculine/feminine) and number (singular/plural). Here it is describing carne, which is a feminine singular noun, so congelado changes to congelada.

Is carne a feminine word even though it ends in -e?

Yes! Nouns ending in -e can be masculine or feminine, so you just have to memorize their gender. Carne is feminine, which is exactly why it forces the adjective to become congelada here.

Why don't we need the word la before carne?

Just like in English, when you are talking about an unspecified amount of something, you can leave the article out. Saying tienen la carne congelada would mean they have the specific frozen meat we were already talking about, rather than just some frozen meat.